/*
 * Copyright (c) Hunan University.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef DERIVATIVE_H_
#define DERIVATIVE_H_

#include "common.h"

namespace nlcpp {
	template<typename Domain, typename Region>
	using DifferentiationType = decltype(std::declval<Domain>() / std::declval<Region>());

	class Differentiation
	{
	public:
		template<typename Domain, typename Region>
		static DifferentiationType<Domain, Region> symmetric_differentiate(Function<Domain, Region> func, Region x, Region h = 1e-6) {
			static_assert(std::is_floating_point<Region>::value,
				"Region type must be floating point.");
			static_assert(std::is_floating_point<Domain>::value,
				"Domain type must be floating point.");

			return (func(x + h) - func(x)) / h;
		}

		template<typename Domain, typename Region>
		static DifferentiationType<Domain, Region> differentiate(Function<Domain, Region> func, Region x, Region h = 1e-6) {
			static_assert(std::is_floating_point<Region>::value,
				"Region type must be floating point.");
			static_assert(std::is_floating_point<Domain>::value,
				"Domain type must be floating point.");

			return (func(x + h) - func(x - h)) / (2 * h);
		}
	};
} // namespace nlcpp

#endif
